The present invention relates in general to the reduction of exterior noise entering the interior of an automotive vehicle, and more specifically to a noise absorbing cover for a loudspeaker.
Noise, vibration, and harshness (NVH) performance is a critical concern in the design of passenger cars and trucks. The primary sources of objectionable noise during driving conditions are road and wind noise originating outside of the vehicle passenger compartment.
Various structures and materials have been employed to block sound energy from entering the passenger compartment such as noise absorbing sheets installed inside vehicle doors and other body panels. Molded cotton or synthetic fiber sheets are often used for their light weight and high coefficient of sound absorption.
Electromechanical speakers are typically mounted in the interior sides of the same vehicle doors and body panels (e.g., rear quarter-panels) that contain noise absorbing sheets. Since the speaker freely transmits sound through its mounting hole, the importance of the noise absorbing sheet at that location is even greater. Thus, prior art noise absorbing sheets have included an integral chamber to receive the rear portion of the speaker.
During operation of the speaker, however, the chamber becomes pressurized because the noise absorbing sheet also blocks the flow of air produced by the vibrating cone of the speaker. The pressurized chamber attenuates the sound production of the speaker at low frequencies, thereby creating a reduction in bass output in the reproduced audio.